That definitely doesn't apply to Bluefin. I can't rule out it applying to effectful, but it is careful to do dynamic checks to make sure you can't use effects in the wrong scope. Maybe you're thinking of eff (i.e. what started this thread)? Alexis King described how to get it to segfault in this video: https://www.twitch.tv/videos/1163853841 (now private, sadly).